Potassium isotope anomalies in meteorites inherited from the protosolar molecular cloud.

Potassium (K) and other moderately volatile elements are depleted in many solar system bodies relative to CI chondrites, which closely match the composition of the Sun. These depletions and associated isotopic fractionations were initially believed to result from thermal processing in the protoplanetary disk, but so far, no correlation between the K depletion and its isotopic composition has been found. Our new high-precision K isotope data correlate with other neutron-rich nuclides (e.g., Ni and Cr) and suggest that the observed K variations have a nucleosynthetic origin. We propose that K isotope anomalies are inherited from an isotopically heterogeneous protosolar molecular cloud, and were preserved in bulk primitive meteorites. Thus, the heterogeneous distribution of both refractory and moderately volatile elements in chondritic meteorites points to a limited radial mixing in the protoplanetary disk.